Discount for six items bought together

I need to set up a discount for any six items from one category when bought together. Is there a way to do this?

More specifically, I have a category containing thirty different greetings cards, and I want to apply a discount for any six of these cards bought together (not just one kind). I can't see a way of doing this using discounts. I have tried to set it up as a separate product, using characteristics to offer a choice of cards, but every time I get past three characteristics the product page is blank (and anyway, that method will mean a lot of work every time a new card is added to the category). Is what I'm trying to do even possible? If so, could anyone advise about the best way to do it?

Hi,

This is possible with "Coupons" not with "Discounts", in the coupons parameters you can set a minimum product quantity and restrict the coupon for a certain category.
So a coupon can be applied to the greeting cars category and if the is minimum 6 products in the cart.

You can enable the "auto load coupon in cart" option to load it automatically.

Ah, I see! Thank you very much, Xavier - that makes perfect sense. I didn't understand what the 'auto load coupon in cart' function was for, but you have made it clear.